The invention relates to bed mattresses, and in particular, to mattresses incorporating a foam construction to enhance the firmness of the perimeter edge support of such mattresses.
Mattresses are formed with a firmer perimeter edge to permit a person to sit on the edge of the mattress. The firmer edge also provides additional support that better enables a person to get up from the mattress. Without a firmer perimeter edge, the coil springs commonly found in mattress constructions to provide cushioning support for a reclining person generally would sag at the perimeter. Various approaches for providing a firmer perimeter edge, while not unnecessarily increasing the firmness of the entire mattress, have been suggested in the art.
One approach is disclosed in U.S. Pat. No. 5,704,085. The ""085 patent discloses a mattress with an edge support formed by a foam layer 23 with an edge firming means as one of the upholstery topper layers. The foam layer 23 is framed by a firming edge 32 to form an edge firming perimeter. The foam layer 23 and firming edge 32 are joined together with glue or adhesive 34. The firming edge 32 is formed from a foam that is firmer than the foam layer 23. The cutting and joining are precisely controlled, and can be difficult to perform because the softer foam layer 23 is more pliable and bendable than the firming edge 32. In addition, the glue adds cost and can form a hard spot in the construction. Moreover, in time, the edges that have been glued together can separate allowing undesired shifting within the mattress construction.
The invention comprises an improvement to the mattress with a foam layer construction shown in U.S. Pat. No. 5,704,085. A mattress according to the invention incorporates an innerspring, at least one upholstery layer provided adjacent to the innerspring, at least one quilt panel layer provided adjacent to the at least one upholstery layer and a foam construction provided within the at least one upholstery layer wherein said foam construction has foam forming an edge about its perimeter that is firmer than foam of a central portion of said foam construction. The foam construction is formed from a first foam layer having a thickness greater at its perimeter and lesser at its central portion, said central portion forming a receiving space, and a second foam layer insertable within the receiving space in the first foam layer. The first foam layer has a firmness greater than the second foam layer. The second foam layer nests within the receiving space in the first foam layer. In the preferred embodiment, the second foam layer fittedly nests within the receiving space such that frictional forces between the contacting surfaces of the first and second foam layers are sufficient to maintain the second foam layer within the receiving space without applied adhesive.
Preferably, the first and second foam layers are formed from polyurethane foam, rebond foam or polyethylene foam. Polyurethane foam is most preferred. For the first foam layer, the foam preferably should have an IFD25 in the range of 100-150. For the second foam layer, the foam preferably should have an IFD25 in the range of 15-45.
The second foam layer has a top surface and a bottom surface and a thickness defined between the top surface and the bottom surface. The receiving space in the first foam layer has a depth defined from the bottom inner surface of the receiving space to the top surface of the first foam layer. The second foam layer preferably has a thickness that substantially matches the depth of the receiving space within the first foam layer. Thus, in such preferred embodiment, the foam construction formed by the first and second foam layers has a constant, or nearly constant, thickness along its entire length. In another embodiment, the thickness of the second foam layer exceeds the depth of the receiving space in the first foam layer to provide greater cushioning or other functionality to the portion of the mattress away from the perimeter edge. Different support characteristics may also be achieved by removing material from the top surface of the second foam layer, such as by convolute cutting or other shaping methods.